Insulation structure transformer windings

ABSTRACT

Corrugated spacers are disposed between winding layers of a transformer winding to enable circulation of air between the layers. Elongated reinforcing rods are placed in corrugations at the corner regions of the winding and adjacent wedges between the winding and the transformer core. Dielectric sheaths of relatively high dielectric constant are disposed between the outermost and innermost winding layers while relatively low dielectric constant sheaths are placed between adjacent pairs of interior layers, thereby to equalize the distributed capacitance between adjacent layers. A dielectric barrier between the high and low voltage windings of a transformer consists of a sheath of dielectric layers wherein the inner and outermost layers have a higher dielectric constant than the interior layers.

atent Jan. 23, 1973 [541 INSULATION STRUCTURE TRANSFORMER WINDINGS HansJ. Weber, Cornwells Heights, Pa.

l-T-E Imperial Philadelphia, Pa.

Filed: March 24, 1972 Appl. No.: 237,714

Inventor:

[73] Assignee: Corporation,

0.8. Cl ..336/70, 336/206 Int. Cl ..H01t 15/14, HOlf 27/32 Field ofSearch ..336/69, 70, 185, 206

[56] References Cited Koch ..3 36/206 Liberman Howlett ..336/206 X a; a24/ Iv Primary Examiner-Thomas J. Kozma Attorney-Sidney G. Faber et a1.

Corrugated spacers are disposed between winding layers of a transformerwinding to enable circulation of air between the layers. Elongatedreinforcing rods are placed in corrugations at the corner regions of thewinding and adjacent wedges between the winding and the transformercore. Dielectric sheaths of relatively high dielectric constant aredisposed between the outermost and innermost winding layers whilerelatively low dielectric constant sheaths are placed between adjacentpairs of interior layers, thereby to equalize the distributedcapacitance between adjacent layers. A dielectric barrier between thehigh and low voltage windings of a transformer consists of a sheath ofdielectric layers wherein the inner and outermost layers have a higherdielectric constant than the interior layers.

ABSTRACT 9 Claims, 9 Drawing Figures wgmgnmea ma sum 3 [IF 3 INSULATIONSTRUCTURE TRANSFORMER WINDINGS RELATED APPLICATIONS This applicationrelates to copending application Ser. No. 237,639 filed Mar. 24, 1972entitled Transformer Winding Structure Using Corrugated Spacers in thenames of Weber and Ruckel and assigned to the assignee of the presentinvention, and which claims aspects of the mechanical structure andsupport of the transformer winding of the present invention.

BRIEF SUMMARY OF THE INVENTION This invention relates to the novelarrangement of dielectric sheaths used in the insulation of transformertype windings in order to obtain a more linear distribution of impulsevoltage between transformer winding layers, and to decrease thedielectric stress on the barrier between high and low voltage windings.

A conventional winding structure for use in an electromagnetic devicesuch as a reactor or transformer consists of a plurality of concentriclayers of windings having a generally equal spacing with identicaldielectric sheaths disposed between adjacent layers. It has been foundthat the first and last of these layers have a distributed capacitanceto their adjacent windings which is lower than the capacitance betweenadjacent interior windings. Consequently, when an impulse voltageappears across the full winding, and is distributed between layers ofthe winding in accordance with their capacitive impedance, a highervoltage stress will appear on the first and last layers, than betweeninterior layers. Thus the danger of a dielectric breakdownat the firstand last layers of the winding under impulse voltage stress isincreased.

In accordance with a first aspect of this invention, the dielectricsheath which insulates the first and last winding layers from theiradjacent layers has a higher dielectric constant than the dielectricsheaths between adjacent interior layers. Therefore, the distributedcapacitance of the first and last layers is increased, as compared tothe distributed capacitance of the interior layers, so that a relativelysmaller percentage of the full impulse voltage will appear across thefirst and last layers and impulse voltage distribution between layerswill be more equal than where the same dielectric sheath material isused between all winding layers.

In accordance with a second aspect of the invention, the dielectricbarrier sheath between high and low voltage windings is made of acomposite of layers of low dielectric constant material sandwichedbetween outer, relatively high dielectric constant material. Thus, suchbarriers are conventionally formed of a common dielectric material ofrelatively low dielectric constant. In accordance with this aspect ofthe invention, however, the dielectric field lines will be spread apartand thus, the dielectric field gradient will be reduced. This thenallows a reduction in the space between the high and low voltagewindings, thereby saving material costs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates athree-phase transformer which has three windings, which could beconstructed in accordance with the present invention.

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FIG. 2 schematically illustrates one high voltage winding of thetransformer of FIG. 1.

FIG. 3a is an end elevational view of one end of a transformer such asthe one of FIG. 1 which incorporates a coil having a construction whichuses the present invention.

FIG. 3b is a partial side elevational view of FIG. 3a.

FIG. 4 is a cross-sectional view of FIG. 3a and is taken across sectionline 4-4 in FIG. 3a.

FIG. 5 is an enlarged view of a portion of FIG. 4 to illustrate theconstruction of the corrugation spacer.

FIG. 6 is an enlarged view, in perspective, of a portion of thehigh-voltage to low-voltage barrier shown in FIG. 4.

FIG. 7 is an enlarged view of a winding corner of FIG. 4 to illustratethe placement of rods and wedges in the winding support structure.

FIG. 8 schematically represents the distributed capacitances affectingthe distribution of impulse voltage across the coil layers of a highvoltage winding.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 partly schematicallyillustrates a conventional transformer which may use the presentinvention in its winding structure. The transformer of FIG. I includes amagnetic core having three core legs 10, 11 and 12 joined by upper yoke13 and lower yoke 14. The core may be made of conventional stackedlaminations, and legs 10, l1 and 12 can be of any desired cross-section,which conventionally is generally rectangular. Each of core legs 10, 11and 12 carry respective low voltage windings 20, 21 and 22 which arewound concentrically with outer high voltage windings 23, 24 and 25. Thehigh and low voltage windings 20 to 25 may be arranged in any desiredmultiphase connection. The invention herein involves the specificconstruction of a winding which may be used in the transformer of FIG.1, when the winding may be air cooled. It is to be noted, however, thatthe invention herein may be used for any type electrical winding, whichis used in any type electromagnetic device.

While any terminal construction could be used for the various windings,each winding is shown in FIG. I as having a simple pair of terminals.FIG. 2 schematically shows that winding 25, for example, may have aplurality of tap terminals 30 to 34, and a second terminal 35. FIG. 2further schematically illustrates the winding 25 as constructed of aplurality of identical layers of windings 36 to 43, and an end layer 44which contains the taps 30 to 34. The schematically shown wound layers36 to 43 are wound over an insulation barrier 45 to be later described,and which insulate the high voltage and low voltage windings. Taps 30 to34 may be made in any desired manner. By way of example, one suitabletap arrangement is shown in copending application, Ser. No. 167,l74,filed July 29, l97l, in the name of Ruckel et al.

FIG. 3a is an end view of the transformer of FIG. 1 when adapted with awinding construction made in accordance with the present invention,while FIG. 3b is a side-elevational view of FIG. 3a and specificallyshows one winding and the taps 30 to 34 of the winding (winding 25 ofFIG. 1). The winding construction as seen in FIGS. 3a and 3b shows theexternal high voltage winding 25, and protruding above and below thehigh voltage winding 25 is the high voltage to low voltage barrier 36a.A low voltage winding, not shown in FIGS. 3a and 3b, is contained withinthe barrier 36a and is wound concentrically with winding 25 on the coreleg 12 of the transformer. The winding structure of the invention ismost clearly shown in cross-section in FIG. 4.

FIG. 4 illustrates the square configuration of core leg 12 where it willbe understood that core leg 12 could also have other configurations, ifdesired. The core leg 12 has wrapped thereon a glass tape layer 50 toinsure insulation integrity between the grounded core and the winding tobe connected thereon. The full winding is wound on a winding machineseparately from the core and, in the embodiment herein, consists of alow voltage winding contained within the interior of the overall windingstructure and an outer high voltage winding. The low voltage windingshown in FIG. 4 has an interior, upwardly extending terminal 51 whichextends beyond the upper end of the winding, and may consist of aconductive foil 52 wound around an axis to form nine turns, whichterminate in terminal 53. Note that terminals 52 and 53 correspond tothe pair of terminals shown for the low voltage winding 22 in FIG. 1.The height of the low voltage winding is generally shown in dotted linesin FIG. 3a, with the low voltage winding 22 being contained within theinsulation barrier 36a. A suitable insulation layer will be used overthe surface of the material used for the low voltage winding. By way ofexample, a layer of asbestos reinforced with glass may be used toinsulate the low voltage winding.

The insulation barrier 36a is then wound around the exterior of the lowvoltage winding 22 where the insulation barrier 36a consists of acomposite of high dielectric and low dielectric layers, most clearlyshown in FIG. 6. Thus, in FIG. 6, the barrier 36a consists of two outerlayers 60 and 61 of a relatively high dielectric constant material with,for example, 14 interior layers 62 of a relatively low dielectricconstant material. Good results have been obtained when using micahaving a thickness of about 0.010 inch for the outer layers 60 and 61,and using a lower dielectric constant material, such as a material knownas Nomex M, having a thickness of 0.010 inch for each of the l4 interiorlayers 62. Nomex M is a trademark of DuPont, and generally is acomposite of nylon and mica.

By using materials of a relatively high dielectric constant in the areaof high dielectric stress between the high and low voltage windings, thedielectric field lines distributed between layers 60 and 61 of FIG. 6will be relatively spread apart thereby to decrease the dielectricgradient. Thus, it is possible to reduce the space between the high andlow voltage windings, thereby saving material costs.

The high voltage winding 25 is then wound on top of the barrier 36a andconsists of the nine layers 36 to 44,

wherein the layers 36 and 42 may each contain 53 turnsof aluminum wirewhich can, for example, have a crosssection of 0.115 by 0.375, whichwire is appropriately insulated. Layer 43 may then have 49 turns, whilethe outer layer 44, which contains the taps 30 to 34,, may have 48turns. It will be noted that a start terminal (terminal 35 in FIG. 1)will come from the first layer 36, while the second terminal of the highvoltage winding 25 in FIG. 1 could, for example, be the tap terminal 34of FIG. 2.

In order to provide appropriate air cooling, whether forced air cooling,or natural convection cooling, each of the winding layers of both thehigh voltage and low voltage windings are spaced by insulationcorrugated spacers. By way of example, corrugated spacers and 71 aretypically shown, respectively, between the first and second, and secondand third windings of the low voltage winding 22. These corrugatedspacers are shown in more detail in FIG. 5, where it is seen that theyhave an undulating configuration which defines side-by-side air channelswhich extend along the full length of the winding layers. Preferably,the corrugations will have a total thickness or excursion of at leastthree-eighths inch in order to define sufficiently large area airchannels to allow a copious flow of cooling air through the channels.

In addition, these corrugations are made of a material which is capableof withstanding the relatively high temperature rise of a dry-type orair-cooled transformer. Good results have been obtained withcorrugations made of polyimid resins, such as Gemon-L, made by theGeneral Electric Corporation. Other suitable materials are moldablematerials, such as Glastic 200, made by the Glastic Corporation, or HST,made by the Haysite Corporation. The material thickness of thesecorrugations may be about one thirty-second inch to provide satisfactorymechanical strength over most of the area of the corrugations. It willbe noted that these corrugations could be crushed at high stress levelsof the winding, but this problem is solved through the use of novelreinforcing rods to be described hereinafter.

Corrugations similar to corrugations 70 and 71 are disposed between eachof the winding layers of the low voltage winding, although if desired,corrugations between only selected pairs of layers could be used. In thepreferred embodiment of the invention, however, and as shown in FIGS. 4and 5, corrugation spacers are provided between each of the foil windinglayers 72, 73 and 74, as well as the remaining foil layers. It should bespecifically noted that the corrugation region is made on selectedperipheral portions of the coil which are disposed externally of theplanes defined by the sides of yokes l3 and 14. In this manner, a clearair passage from the bottom of the transformer to the top is definedwithout interference from the yokes of the transformer.

A similar arrangement of corrugation spacers of identical material tospacers 70 and 71 is provided for the high voltage winding. Thus,corrugation spacers such as spacers 75 and 76 are disposed betweenwinding layers 36 and 37, and 37 and 38, respectively. Similarvcorrugation structures are provided between each of the other windinglayers of the high voltage winding. It will be seen that the corrugationspacer used for the high voltage winding also define air channels on theoutside of the yokes of the transformer, thereby to provide clearunrestricted air-flow channels through which cooling air may be carried.

In addition, and in the winding shown in FIG. 4, corrugation spacers 77and 78 are formed in the region passing between the yokes l3 and 14 ofthe transformer, and between winding layers 38 and 39 to help conductheat from this interior portion of the winding even though the coolingair path will be partly blocked by the yokes l3 and 14.

As pointed out previously, the corrugation structure is sufficientlystrong to maintain its configuration and physical strength in most partsof the coil. However, in high stress regions, it is possible that thecorrugation could be crushed. In order to prevent the local crushing ofthe corrugation, and as shown in FIG. 4, the corner regions at which thewinding layers bend are reinforced by insulation rods disposed withinthe corrugation and adjacent the corner region. Typical insulation rodsare shown as rods 80, 81, 82, 83 and 84, which are generally disposed atthe last corrugation region of their respective corrugation spacers, andat the region where the winding layer turns a corner. The insulationrods will then support and prevent the corrugation from collapsingduring winding and extend the full length of the corrugation and may besecured thereto as by gluing.

The outer diameter of these rods will be approximately equal to theexcursion of the corrugation. Thus, in FIG. 7, rods 85 and 86 may have adiameter of approximately five-sixteenths inch where the corrugationsmight have a total excursion, or total thickness, from peak to peak ofthree-eighths inch, and a wall thickness of one thirty-second inch.

In order to assemble the completely wound winding on the core 12, theupper yoke member 13 is disassembled in standard fashion, and the totalwinding. is mounted concentrically with the winding leg 12, and issecured in place on the winding leg.l2 by appropriate mountingstructures, which could include insulation wedge members, such as thewedge members 90 to 95 shown in FIG. 4. These insulation wedges aresimply elongated sticks which may be slightly wedge-shaped and which areforced between the interior of the winding and the exterior of the coreleg 12. It has been found useful to dispose reinforcing rods in thefirst corrugation 70 at regions adjacent these wedge members to preventlocal collapse of the interior corrugation 70.

Thus, in FIG. 4 it is seen that insulation rods, for example, rods 96and 97 are placed adjacent the wedges 91 and 92 to prevent localcollapse of the corrugation 70 at these regions.

A further important feature of the winding structure of FIG. 4 consistsof the use of selective dielectric layers between the winding layersforming thehigh voltage winding. Thus, as shown in FIG. 4, a dielectricsheath or layer of tape is formed between each of the winding layersThese dielectric sheaths consist, for example, of the sheaths 101 to109.

In accordance with an important feature of the present invention, theinner and outermost sheaths I01 and 109 of the high voltage winding aremade of a material having a dielectric constant which is higher than thedielectric constant of the interior dielectric sheaths 102 to 108. Thus,each of the winding layers 36 to 44 may be equally spaced, for example,by threeeighths inch, but the insulation sheaths 102 to 108 are formedof two layers of 0.0l inch thick Nomex M, while the exterior insulationlayers 101 and 109 are formed of, for example, two layers of 0.010 inchthick mica. With this structure, materials of higher dielectric constantare disposed between the first and last layers of the high voltagewinding, thereby to increase the distributed capacitance of the firstand last layers of the transformer winding in order to substantiallyequalize the capacitance between all layers in order to cause equalvoltage distribution of an impulse voltage applied to the high voltagewinding.

This construction can be better understood in connection with FIG. 8,which schematically illustrates the high voltage winding 25 inconnection with its distributed capacitances. Thus, there is animaginary neutral plane shown by the dotted lines N between each pair ofadjacent winding layers, with the distributed capacitance betweenwinding layers being schematically illustrated as capacitances connectedfrom the winding to the neutral plane. The total winding will be coupledto ground through the equivalent capacitances C, and C However, theequivalent layer capacitances of the first layer 36 to the second layer37 and of the outer layer 44 to the next innermost layer 43 will be acapacitance C which is smaller than the distributed capacitances Cbetween the remaining interior adjacent layers 37 to 43. Consequently,an impulse voltage applied to the high voltage winding could, forexample, due to the effect of a lightning stroke, not distribute equallybetween the winding layers, but rather a larger percentage of thevoltage will appear between layers 36 and 37, and 43 and 44, thanbetween the adjacent layers.

In accordance with the present invention, and by using higher dielectricconstant material between the first and last pairs of layers, theequivalent capacitance between these layers is increased to a valueapproaching that of the distributed capacitance between the remaininginterior layers, thereby to improve the voltage distribution patternacross the winding due to impulse voltages. Note that this selection ofdifferent dielectric constant materials allows the transformer windingconstruction to use identical interlayer spacing thereby simplifying themanufacture of the transformer. Clearly, other combinations ofdielectric materials could have been selected, if desired.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. A winding for an electromagnetic device; said winding comprising acontinuouseonductor wound to form a plurality of turns around an axis;said winding consisting of a plurality of concentric layers; a pluralityI of layers of dielectric material, each disposed between adjacent pairsof concentric layers of said winding; first and second layers of saidplurality of layers of dielectric material disposed between theoutermost pair and innermost pair of winding layers having a higherdielectric constant than the remaining dielectric layers disposedbetween adjacent interior layers of said windmg.

2. The winding of claim 1 wherein the distributed capacitance betweeneach adjacent pair of winding layers is approximately equal.

3. The winding of claim 1 wherein each of said winding layers issubstantially identical in construction and wherein each of said layersis spaced from adjacent layers by an identical spacing; said first andsecond dielectric layers having a dielectric constant which issufficiently high to increase the distributed capacitance of saidexterior and interior pairs of winding layers to a value substantiallyequal to the distributed capacitance between the said interior windinglayers which are insulated by relatively lower dielectric constantlayers of dielectric material.

4. A transformer winding comprising, in combination:

a plurality of substantially identical concentric winding layersconnected in circuit relation with one another; I

a plurality of layers of dielectric material, said plurality of layersof dielectric material respectively disposed between respective adjacentpairs of said winding layers and being concentric and coextensive withsaid respective pairs of winding layers;

the outermost and innermost of said layers of dielectric material,disposed respectively between the outermost and innermost pairs ofadjacent winding layers, and having a higher dielectric constant thanthe remaining layers of said plurality of layers, thereby to make thedistributed capacitance between each pair of adjacent winding layersapproximately equal.

5. The transformer winding of claim 4 wherein each of said adjacentpairs of winding layers has an approximately equal spacing.

6. An electrical transformer comprising, in combination:

a magnetic core structure;

a low voltage winding wound on said magnetic core structure;

a high voltage winding wound on said core structure and concentric withsaid low voltage winding;

said high voltage winding comprising a plurality of substantiallyidentical concentric winding layers connected in circuit relation withone another;

a plurality of layers of dielectric material, said plurality of layersof dielectric material respectively disposed between respective adjacentpairs of said winding layers and being concentric and coextensive withsaid respective pairs of winding layers;

the outermost and innermost of said layers of dielectric material,disposed respectively between the outermost and innermost pairs ofadjacent winding layers, and having a higher dielectric constant thanthe remaining layers of said plurality of layers, thereby to make thedistributed capacitance between each pair of adjacent winding layersapproximately equal.

7. The transformer winding of claim 6 wherein each of said adjacentpairs of winding layers has an approximately equal spacing.

8. The combination of claim 6 which further includes a dielectricbarrier sleeve disposed concentrically with and between said high andlow voltage windings; said dielectric barrier comprising a plurality ofconcentric layers of dielectric material which include outer layers ofrelatively high dielectric constant material and a plurality of innerlayers of a relatively lower dielectric material.

9. An electrical transformer comprising, in combination:

a magnetic'core structure;

a low voltage winding wound on said magnetic core structure;

a high voltage winding wound on said core structure and concentric withsaid low voltage winding;

said high voltage winding comprising a plurality of substantiallyidentical concentric winding layers connected in circuit relation withone another;

a plurality of layers of dielectric material, said plurality of layersof dielectric material respectively disposed between respective adjacentpairs of said winding layers and being concentric and coextensive withsaid respective pairs of winding layers;

and a dielectric barrier sleeve disposed concentrically with and betweensaid high and low voltage windings; said dielectric barrier comprising aplurality of concentric layers of dielectric material which includeouter layers of relatively high dielectric constant material and aplurality of inner layers of a relatively lower dielectric constantmaterial.

1. A winding for an electromagnetic device; said winding comprising acontinuous conductor wound to form a plurality of turns around an axis;said winding consisting of a plurality of concentric layers; a pluralityof layers of dielectric material, each disposed between adjacent pairsof concentric layers of said winding; first and second layers of saidplurality of layers of dielectric material disposed between theoutermost pair and innermost pair of winding layers having a higherdielectric constant than the remaining dielectric layers disposedbetween adjacent interior layers of said winding.
 2. The winding ofclaim 1 wherein the distributed capacitance between each adjacent pairof winding layers is approximately equal.
 3. The winding of claim 1wherein each of said winding layers is substantially identical inconstruction and wherein each of said layers is spaced from adjacentlayers by an identical spacing; said first and second dielectric layershaving a dielectric constant which is sufficiently high to increase thedistributed capacitance of said exterior and interior pairs of windinglayers to a value substantially equal to the distributed capacitancebetween the said interior winding layers which are insulated byrelatively lower dielectric constant layers of dielectric material.
 4. Atransformer winding comprising, in combination: a plurality ofsubstantially identical concentric winding layers connected in circuitrelation with one another; a plurality of layers of dielectric material,said plurality of layers of dielectric material respectively disposedbetween respective adjacent pairs of said winding layers and beingconcentric and coextensive with said respective pairs of winding layers;the outermost and innermost of said layers of dielectric material,disposed respectively between the outermost and innermost pairs ofadjacent winding layers, and having a higher dielectric constant thanthe remaining layers of said plurality of layers, thereby to make thedistributed capacitance between each pair of adjacent winding layersapproximately equal.
 5. The transformer winding of claim 4 wherein eachof said adjacent pairs of winding layers has an approximately equalspacing.
 6. An electrical transformer comprising, in combination: amagnetic core structure; a low voltage winding wound on said magneticcore structure; a high voltage winding wound on said core structure andconcentric with said low voltage winding; said high voltage windingcomprising a plurality of substantially identical concentric windinglayers connected in circuit relation with one another; a plurality oflayers of dielectric material, said plurality of layers of dielectricmaterial respectively disposed between respective adjacent pairs of saidwinding layers and being concentric and coextensive with said respectivepairs of winding layers; the outermost and innermost of said layers ofdielectric material, disposed respectively between the outermost andinnermost pairs of adjacent winding layers, and having a higherdielectric constant than the remaining layers of said plurality oflayers, thereby to make the distributed capacitance between each pair ofadjacent winding layers approximately equal.
 7. The transformer windingof claim 6 wherein each of said adjacent pairs of winding layers has anapproximately equal spacing.
 8. The combination of claim 6 which furtherincludes a dielectric barrier sleeve disposed concentrically with andbetween said high and low voltage windings; said dielectric barriercomprising a plurality of concentric layers of dielectric material whichinclude outer layers of relatively high dielectric constant material anda plurality of inner layers of a relatively lower dielectric material.9. An electrical transformer comprising, in combination: a magnetic corestructure; a low voltage winding wound on said magnetic core structure;a high voltage winding wound on said core structure and concentric withsaid low voltage winding; said high voltage winding comprising aplurality of substantially identical concentric winding layers connectedin circuit relation with one another; a plurality of layers ofdielectric material, said plurality of layers of dielectric materialrespectively disposed between respective adjacent pairs of said windinglayers and being concentric and coextensive with said respective pairsof winding layers; and a dielectric barrier sleeve disposedconcentrically with and between said high and low voltage windings; saiddielectric barrier comprising a plurality of concentric layers ofdielectric material which include outer layers of relatively highdielectric constant material and a plurality of inner layers of arelatively lower dielectric constant material.